Trump will also have to get that 25 or 30 percent to go to the polls. For now, most surveys cover Republican-leaning adults or registered voters, rather than likely voters. Combine that with the poor response rates to polls and the fact that an increasing number of polls use nontraditional sampling methods, and it’s not clear how much overlap there is between the people included in these surveys and the relatively small share of Republicans who will turn up to vote in primaries and caucuses.

But there’s another, more fundamental problem. That 25 or 30 percent of the vote isn’t really Donald Trump’s for the keeping. In fact, it doesn’t belong to any candidate. If past nomination races are any guide, the vast majority of eventual Republican voters haven’t made up their minds yet.

It can be easy to forget it if you cover politics for a living, but most people aren’t paying all that much attention to the campaign right now. Certainly, voters are consuming some campaign-related news. Debate ratings are way up, and Google searches for topics related to the primaries1 have been running slightly ahead of where they were at a comparable point of the 2008 campaign, the last time both parties had open races. But most voters have a lot of competing priorities. Developments that can dominate a political news cycle, like Trump’s frenzied 90-minute speech in Iowa earlier this month, may reach only 20 percent or so of Americans.

We can look deeper into the Google search data for some evidence of this. In the chart below, I’ve tracked the aggregate share of primary-related searches in the 2008 and 2012 presidential cycles, based on the number of weeks before or after the Iowa caucuses.2 As you can see, public attention to the race starts out quite slow and only gradually accelerates — until just a week or two before Iowa, when it begins to boom. Interest continues to accelerate as Iowa, New Hampshire and the Super Tuesday states vote, before slowing down again once the outcome of the race has become clear.

To repeat: This burst of attention occurs quite late — usually when voters are days or weeks away from their primary or caucus. At this point in the 2012 nomination cycle, 10 weeks before the Iowa caucuses, only 16 percent of the eventual total of Google searches had been conducted. At this point in the 2008 cycle, only 8 percent had been. Voters are still in the early stages of their information-gathering process.

When should you start paying attention to the polls?

But maybe you don’t trust the Google search data. That’s OK; exit polls like this one have historically asked voters in Iowa and New Hampshire when they made their final decision on how to vote. These exit polls find that voters take their sweet time. In Iowa, on average, only 35 percent of voters had come to a final decision before the final month of the campaign. And in New Hampshire, only 29 percent had. (Why is the fraction lower in New Hampshire than in Iowa? Probably because voters there are waiting for the Iowa results before locking in their choice. In fact, about half of New Hampshire voters make up their minds in the final week of the campaign.)

SHARE OF IOWA VOTERS WHO DECIDED

ELECTION

> 1 MONTH OUT

1 WEEK TO 1 MONTH OUT

FINAL WEEK

2004 Democrats

30%

27%

42%

2008 Republicans

28

31

40

2008 Democrats

49

24

27

2012 Republicans

32

21

46

Iowa Average

35

26

39

SHARE OF N.H. VOTERS WHO DECIDED

ELECTION

> 1 MONTH OUT

1 WEEK TO 1 MONTH OUT

FINAL WEEK

2004 Democrats

26%

19%

54%

2008 Republicans

29

22

50

2008 Democrats

34

17

48

2012 Republicans

28

26

46

New Hampshire Average

29

21

50

By comparison, voters decide much earlier in general elections. In Ohio in 2012, for example, 76 percent of voters had settled on Mitt Romney or Barack Obama by the end of September. This is why it’s common to see last-minute surges or busts in nomination races (think Rick Santorum or Howard Dean), but not in general elections.

If even by New Year’s Day (a month before the Iowa caucuses, which are scheduled for Feb. 1) only about one-third of Iowa voters will have come to their final decision, the percentage must be even lower now — perhaps something like 20 percent of voters are locked in. When you see an Iowa poll, you should keep in mind that the real situation looks something more like this:3

CANDIDATE

SUPPORT IN IOWA

Undecided

80%

Donald Trump

5

Ben Carson

4

Ted Cruz

3

Marco Rubio

2

Jeb Bush

1

Carly Fiorina

1

Mike Huckabee

1

Chris Christie

1

So, could Trump win? We confront two stubborn facts: first, that nobody remotely like Trump has won a major-party nomination in the modern era.4 And second, as is always a problem in analysis of presidential campaigns, we don’t have all that many data points, so unprecedented events can occur with some regularity. For my money, that adds up to Trump’s chances being higher than 0 but (considerably) less than 20 percent. Your mileage may vary. But you probably shouldn’t rely solely on the polls to make your case; it’s still too soon for that.

Footnotes

The statistics I describe in this article cover U.S.-based searches for Google search topic “primary elections.” It’s possible that this data includes a small number of searches for non-presidential races such as gubernatorial primaries, but the historical timing of the peaks in the data suggests that the vast majority are related to the presidency.

The chart covers the period from a year before the Iowa caucus to late June of the election year.

The numbers below reflect what you get if you take the Real Clear Politics average, put 80 percent of voters in the undecided category and scale everyone down accordingly.

There are better precedents for candidates like Bernie Sanders and Ted Cruz, who might loosely be compared to George McGovern and Barry Goldwater.

Nate Silver is the founder and editor in chief of FiveThirtyEight. @natesilver538